js 进度条的实现

使用 HTML 和 CSS 创建基础进度条

HTML 结构可以简单使用一个 div 元素作为容器，内部嵌套另一个 div 表示进度：

<div class="progress-container">
  <div class="progress-bar" id="progressBar"></div>
</div>

CSS 样式定义容器和进度条的视觉效果：

.progress-container {
  width: 100%;
  height: 20px;
  background-color: #f0f0f0;
  border-radius: 10px;
  overflow: hidden;
}

.progress-bar {
  height: 100%;
  width: 0%;
  background-color: #4CAF50;
  transition: width 0.3s ease;
}

通过 JavaScript 动态更新进度

使用 style.width 属性动态控制进度条宽度：

function updateProgress(percent) {
  const progressBar = document.getElementById('progressBar');
  progressBar.style.width = percent + '%';
}

// 示例：更新进度到75%
updateProgress(75);

实现动画效果

结合 requestAnimationFrame 实现平滑动画：

function animateProgress(targetPercent, duration = 1000) {
  const progressBar = document.getElementById('progressBar');
  const startTime = performance.now();
  const startWidth = parseFloat(progressBar.style.width) || 0;

  function step(currentTime) {
    const elapsed = currentTime - startTime;
    const progress = Math.min(elapsed / duration, 1);
    const currentWidth = startWidth + (targetPercent - startWidth) * progress;
    progressBar.style.width = currentWidth + '%';

    if (progress < 1) {
      requestAnimationFrame(step);
    }
  }

  requestAnimationFrame(step);
}

// 示例：动画形式过渡到90%
animateProgress(90);

使用 HTML5 <progress> 元素

原生进度条元素更简洁：

<progress id="nativeProgress" value="0" max="100"></progress>

JavaScript 控制：

const progressElement = document.getElementById('nativeProgress');
progressElement.value = 50; // 设置进度为50%

圆形进度条实现

通过 SVG 或 Canvas 实现圆形进度条：

<svg class="circular-progress" viewBox="0 0 36 36">
  <path class="track" d="M18 2.0845 a 15.9155 15.9155 0 0 1 0 31.831 a 15.9155 15.9155 0 0 1 0 -31.831"/>
  <path class="fill" stroke-dasharray="0, 100" d="M18 2.0845 a 15.9155 15.9155 0 0 1 0 31.831 a 15.9155 15.9155 0 0 1 0 -31.831"/>
</svg>

JavaScript 控制：

function updateCircleProgress(percent) {
  const fill = document.querySelector('.fill');
  const circumference = 2 * Math.PI * 15.9155;
  const offset = circumference - (percent / 100) * circumference;
  fill.style.strokeDasharray = `${circumference} ${circumference}`;
  fill.style.strokeDashoffset = offset;
}

updateCircleProgress(75);

进度条事件监听

添加事件监听实现交互：

document.getElementById('progressButton').addEventListener('click', () => {
  let currentProgress = 0;
  const interval = setInterval(() => {
    currentProgress += 5;
    updateProgress(currentProgress);
    if (currentProgress >= 100) clearInterval(interval);
  }, 200);
});